1. Field of the Invention
The present invention relates to a battery state monitoring circuit for detecting a voltage and an abnormality of a secondary battery and a battery device including the battery state monitoring circuit, and more particularly, to a battery state monitoring circuit incorporating a temperature sensor in a charge/discharge control circuit and a battery device including the battery state monitoring circuit.
2. Description of the Related Art
FIG. 3 illustrates a circuit diagram of a conventional battery device incorporating a temperature sensor. The conventional battery device incorporating the temperature sensor includes a secondary battery 101, a battery state monitoring circuit 309, an external terminal 106, and an external terminal 107. The battery state monitoring circuit 309 includes an overcharge detection circuit 301, an overdischarge detection circuit 305, a control circuit 302, an overheat detection circuit 304, a temperature sensor 307, an overcurrent detection circuit 303, a discharge field-effect transistor (FET) 306, a charge FET 308.
Connection is made as follows. The positive terminal side of the secondary battery 101 is connected to the overcharge detection circuit 301, the overdischarge detection circuit 305, and the external terminal 106, and the negative terminal side thereof is connected to a source of the discharge FET 306. The control circuit 302 is connected to an output of the overcharge detection circuit 301, an output of the overdischarge detection circuit 305, an output of the overcurrent detection circuit 303, and an output of the overheat detection circuit 304. The discharge FET 306 has a gate connected to an output of the control circuit 302 and a drain connected to a drain of the charge FET 308. The charge FET 308 has a gate connected to another output of the control circuit 302 and a source connected to an input of the overcurrent detection circuit 303 and the external terminal 107.
When the charge FET 308 enters an abnormal overheated state due to overcurrent during charge, the overheat detection circuit 304 notifies the control circuit 302 of the abnormal state so that the control circuit 302 operates to change the gate of the charge FET 308 to L to disconnect a charge current. Therefore, the charge FET 308 for charge control can be protected from abnormal overheat (see, for example, Japanese Patent Application Laid-open No. 2007-124775).
The battery device needs overheat protection by a temperature sensor circuit even when the secondary battery is charged from 0 V. The temperature sensor circuit obtains power from between the external terminals because, otherwise if the power is obtained from the secondary battery side, the temperature sensor circuit does not operate when the battery voltage is 0 V, and hence the overheat protection does not work. In the conventional technology, however, current consumption of the temperature sensor circuit is a load to an automatic recovery circuit, and hence there is a problem that the automatic recovery circuit cannot operate normally at the time of recovery from an overcurrent protection state using an automatic recovery function. This is because the automatic recovery circuit outputs a minute current so as to suppress consumption of the battery and the output current of the automatic recovery circuit is completely consumed by the overheat detection circuit to hinder the automatic recovery operation.